With the rapid development of modern digital signal processing technology in recent years, continuously the processing capability of a DSP chip is enhanced and the price of the chip is reduced, so that it is possible to form antenna beams at baseband with digital technology, therefore the smart antenna technology with a key technology of an adaptive beam forming algorithm is widely used in CDMA communication.
In a CDMA communication system, accurate time delay information is required before the adaptive beam forming of a smart antenna, otherwise the result of adaptive processing will be influenced seriously due to the correlation of codes. At present, there are many beam forming algorithms for smart antennas, but the common disadvantage of them consists in that it does not solve the problem of multipath time delay. It is supposed that the time delay information is known accurately or that the time delay is known in existing adaptive beam forming algorithms for smart antennas, and this kind of algorithms relate a little detailed embodiments and structures. In the Chinese patent application with a publication number of 1235391, named “Adaptive Array Antenna Optimizing and Forming Beams in Advance for Code Division Multiple Access System”, the calculation of the weight in complex number is divided into two parts, i.e. initial weight designing and operational weight processing, since this application does not solve the problem of time delay accuracy and it requires a high initial weight, the performance of the smart antenna is hardly ensured. Because it is crucial for an adaptive beam forming method to determine the multipath time delay accurately, how to search out the time delay information accurately is a problem which should be solved by the prior arts urgently.